I have an M2.0 Compact and an RM07 on the way.
Do you guys use sealing plates?
According to Trijicon's instructions you're supposed to due to the through feature (strike block hole), but when I google search RMR'd M&Ps it shows tons of pictures of RMRs installed without the sealing plate.

Never used it on my M&P9FS that was milled for an RMR.

I did have to use it on a Glock 34MOS. If I remember correctly, you had to use it on all Glock MOS, but not on the M&P.

But wouldn't the RMR be at risk if the handgun were submerged in water or something?

After thinking about it, I did use the sealing plate on mine. If you look closely you can see the plate. Hope this helps.

I have a G19, G17 and M&P .45 with RMRs. They now all have the sealing plate. For a few years the G17 didn't, to no I'll affect, but when I decided to do a battery change I dropped it in.

I live and shoot in a desert, so moisture is not a major concern, but with then $$ investEd in the base guns, milling and RMRs, it's a cheap add that doesn't seem to have a down side.

True, I just prefer how it looks without the sealing plate. Where'd you guys get your work done? The only place I've found that offers a cover plate (for when used without the RMR) for the M&P is IGFS but I haven't heard anything (good or bad) about their milling services.

I use a simple, thin flat sealing plate to close off the bottom of my two RMR06. The slides are custom milled for the RMR footprint. Each of them is cut as deeply as possible while avoiding interfering with the striker block or extractor locking pin. One is a FS 1.0 and the other a Glock 19.

I avoid any contraption that raises the sight higher. The goal of custom milling is two-fold: lowest possible mounting and most secure mounting for fore and aft forces.

Generic mounting systems that allow different optics are often insecure and because of adapter plates higher than necessary. If an adapter plate has top pins to take the reciprocating forces it can be secure, but it will still be higher than necessary.

Does the 2.0C have a loaded chamber indicator on the top of the slide? If so, that might preclude mounting an optic.

Mine all have sealing plates. If the slide is custom milled the sealing plate is a must, due to the plunger spring . On the core and pro series the spring is contained under a tiny cap with allen screw. In that case the plate helps to prevent the battery from shorting out . It actually works. Lots of people use a piece of electric tape.
Either way it's cheap insurance